1. Field of the Invention
The present invention relates, in general, to general packet radio service systems for providing packet-based wireless communication services and, more particularly, to a method of balancing a load and method of setting up a call using the load balancing method in a general packet radio service network, which solves a phenomenon in which a load concentrates on a specific gateway general packet radio service system supporting node, thus reducing factors which deteriorate the performance of services, such as a failure in session establishment.
2. Description of the Related Art
Recently, in order to extend a data network to a wireless communication network, the concept of General Packet Radio Service (GPRS) has been proposed. GPRS is defined by a high-speed data transmission service provided when a user accesses an Internet Protocol (IP) network and a packet network through a wireless terminal to transmit packet data in a mobile communication system.
The GPRS network allows non-voice information to be added to information transmitted or received through a wireless communication system, and enables a connection to the conventional wired Internet, thus enabling a user to use Internet services at a mobile node, such as a mobile phone or Personal Digital Assistant (PDA) terminal.
FIG. 1 is a view showing the network configuration of an asynchronous mobile communication system including a GPRS network. Reference numerals used in FIG. 1 are defined below.
Reference numeral 110 represents a mobile node used by a user, which corresponds to a mobile phone or PDA terminal. When the user requests the mobile node 110 to access GPRS, the mobile node 110 transmits the request to a higher system, and transmits/receives data by the completion of a session establishment.
Reference numeral 120 represents a wireless network which is a wireless interface section of data transmission/reception channels to the mobile node 110. Reference numeral 130 represents a GPRS network capable of providing packet services to the wireless network 120. The GPRS network 130 includes a Service GPRS Supporting Node (SGSN) 131 for configuring session information in conjunction with a Home Location Register (HLR) 140 and transmitting/receiving data packets to/from the mobile node 110 within a service area, and a gateway GPRS supporting node (GGSN) 132 connected to a Public Domain Network (PDN) 160 to connect between the GPRS network and an external packet network and then enable packet data services to be provided to the mobile node 110 of the user.
Further, reference numeral 140 represents the Home Location Register (HLR), which is a database used to manage various pieces of information, such as terminal information, subscription information, location information and authentication information of a subscriber in wireless communications. Reference numeral 150 represents a Domain Name System (DNS) server, which maintains a database related to domain names and IP addresses corresponding to the domain names, and provides an IP address of a destination in response to a request received from the Service GPRS Supporting Node (SGSN) 131.
Further, reference numeral 160 represents the Public Domain Network (PDN), and 170 represents a correspondent node (CN), which the mobile node 110 connected to the PDN 160 requires to access.
In the above configuration, the SGSN 131 of the GPRS 130 performs functions, such as packet routing and transmission, mobility management, logical link management, authentication and billing. The HLR 140 operated in conjunction with the SGSN 131 stores and manages location information (for example, cell or visitor location register) and user profile information (International Mobile Subscriber Identity: IMSI) of a GPRS subscriber registered in the SGSN 131, etc. Further, the GGSN 132 converts GPRS packets transmitted through a tunnel established with the SGSN 131 into suitable Packet Data Protocol (PDP)-format data (for example, IP, X.25), transmits the PDP-format data to the Correspondent Node (CN) 170 through the PDP network 160, converts a PDP address of packet data received through the PDP network 160 into a Global System for Mobile communications (GSM) address of a GPRS subscriber, converts the corresponding packet data into GPRS data, and transmits the GPRS data to the SGSN 131.
FIG. 2 is a view showing a typical call setup process in the GPRS network of FIG. 1. Referring to FIG. 2, call setup in the GPRS network 130 starts by transmitting an Activate PDP Context Request message from the mobile node 110 requiring a packet data service (that is, GPRS) to the SGSN 131 connected to the wireless network 120 at step S11.
As described above, the SGSN 131 having received the Activate PDP Context Request message from the mobile node 110 selects an accessible GGSN 132 using an Access Point Name (APN) included in the received message, and requests an IP address corresponding to the GGSN 132 from the DNS server 150 at step S12.
Therefore, the DNS server 150 searches for the IP address corresponding to the GGSN 132 and transmits the searched IP address to the SGSN 131 at step S13. The SGSN 131 having received the IP address transmits a Create PDP Context Request message to the GGSN 132 specified by the IP address at step S14. The GGSN 132 having received the Create PDP Context Request message performs resource allocation to the mobile node 110 of the corresponding user in response to the Create PDP Context Request message, and transmits the results of the resource allocation to the SGSN 131 through a Create PDP Context Response message at step S15. Further, the SGSN 131 configures session information on the basis of the contents of the received response message, and transmits an Activate PDP Context Accept message to the mobile node 110 at step S16. Thereafter, the mobile node 110 performs the transmission/reception of packet data to/from the correspondent node 170 through a tunnel allocated between the SGSN 131 and the GGSN 132.
As described above, in order for the mobile node 110 to be provided with GPRS, the PDP context establishment of allocating a tunnel between the SGSN 131 connected to the mobile node 110 and the GGSN 132 connected to the correspondent node 170 should be performed.
At this time, the SGSN 131 must search for GGSNs 132 related to APN included in the Activate PDP Context Request message received from the mobile node 110 and select one among the searched GGSNs 132 so as to create PDP contexts. However, occasionally, there may occur a case in which two or more GGSNs supporting the corresponding APN exist. In prior art, because GGSN is selected according to specified priority regardless of the number of sessions established with each GGSN, the same GGSN may be selected at each time. Therefore, there are problems in that requests for a session establishment concentrate on a specific GGSN, which increases the probability of failure in session establishment.